ABSTRACT What biological traits distinguish taxa susceptible to extinction
from less susceptible taxa? Substantiated island biogeographic theory
suggests that after insularization, small islands lose more species
than do large islands. Thus, susceptible taxa are those now found on
only large islands. The traits of susceptible taxa can thus be found by
comparing the biology of species found only on large islands with those
also found on small islands. The islands examined here are those of the
Sunda Shelf, created as a result of the Holocene rise in sea levels of
120 m. We use four statistical comparisons: comparative analysis by
(phylogenetically) independent contrasts (N = 8 contrasts at the
sub-generic or deeper level), Spearman correlations, stepwise
regression, and principle components analysis (N = 9
sub-genera/genera). The genera and one sub-genus considered are: Hylobates, Macaca, Nasalis, Nycticebus, Pongo, Presbytis, Symphalangus, Tarsius, and Trachypithecus.
Traits of risk appear to be large body mass, low density, large annual
home range, and low maximum latitude. Expected traits that did not
correlate with susceptibility were low interbirth interval, high
percent frugivory, high group mass, low altitudinal range, and small
geographic range. The risky traits also apply to just the anthropoids
(i.e., prosimians excluded). The risky traits are explained if
susceptibility is induced by requirements for a large extent of
habitat, a small population size, and specialization. These findings,
which indicate that efficiency and plasticity of use of the environment
separate susceptible from successful primate taxa, might be relevant to
understanding of hominoid evolution.

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